A particle based simulation model for glacier dynamics

Abstract

Abstract.A particle-based computer simulation model was developed for investigating the dynamics of glaciers. In the model, large ice bodies are made of discrete elastic particles which are bound together by massless elastic beams. These beams can break, which induces brittle behaviour. At loads below fracture, beams may also break and reform with small probabilities to incorporate slowly deforming viscous behaviour in the model. This model has the advantage that it can simulate important physical processes such as ice calving and fracturing in a more realistic way than traditional continuum models. For benchmarking purposes the deformation of an ice block on a slip-free surface was compared to that of a similar block simulated with a Finite Element fullStokes continuum model. Two simulations were performed: (1) calving of an ice block partially supported in water, similar to a grounded marine glacier terminus, and (2) fracturing of an ice block on an inclined plane of varying basal friction, which could represent transition to fast flow or surging. Despite several approximations, including restriction to twodimensions and simplified water-ice interaction, the model was able to reproduce the size distributions of the debris observed in calving, which may be approximated by universal scaling laws. On a moderate slope, a large ice block was stable and quiescent as long as there was enough of friction against the substrate. For a critical length of frictional contact, global sliding began, and the model block disintegrated in a manner suggestive of a surging glacier. In this case the fragment size distribution produced was typical of a grinding process.

Modelling environmental influences on calving at Helheim Glacier in eastern Greenland

“…A similar calving event size was also produced by a recent particle-based model of Helheim Glacier (Bassis and Jacobs, 2013). The approximately normal calving event size distribution produced by the model disagrees with other published studies which observe a power-law type distribution of iceberg sizes, where small ice losses are the most common (Dowdeswell, 1989;Chapuis, 2011;Åström et al, 2013). This difference is to be expected given the mesh resolution of 40 m and time-step of 0.003 yr used in most experiments -this is insufficient to model very small calving events, but able to capture large changes in terminus position which are likely to dominate long-term behaviour.…”

Ice shelf fracture parameterization in an ice sheet model

“…On microscopic scales fracturing is a discrete process which operates on timescales determined by the speed of sound in ice and the rupture speed could be influenced by the local variations of stress state and material properties (Ye et al, 2016). Combining these processes in a single model presents very difficult nu-merical challenges that have only been attempted for a few cases using discrete element models (Bassis and Jacobs, 2013;Åström et al, 2013. This discrete approach has a firm basis in physics with, for example, Glen's flow law emerging naturally.…”

Combining damage and fracture mechanics to model calving

“…Another approach to modelling calving uses discreteelement models (Bassis and Jacobs, 2013;Åström et al, 2013). This type of model has produced interesting results in terms of calving processes and iceberg size distribution.…”